The present invention generally relates to a method and apparatus for removing electrostatically bonded powder coating material from a non-recessed region of a surface of a workpiece without removing powder coating material from a recessed region of the surface of the workpiece.
It has heretofore not been possible to take a workpiece having powder coating material electrostatically bonded to both recessed and non-recessed regions thereof and to remove in an efficient and practical manner the powder coating material on the non-recessed region without also removing the powder coating material from the recessed region. Consequently, it has not been possible to employ in an efficient and practical manner a powder coating process to coat both a non-recessed region of a workpiece with coating material of a first color and to subsequently coat a recessed region of the workpiece with coating material of a second color.
An example of a process employed in the prior art to coat a workpiece having non-recessed and recessed regions comprises applying a first layer of powder coating material of a first color over the entire outer surface of the workpiece and thereafter curing the coating material in an oven. A section of the outer surface of the workpiece, including the recessed region, is then masked off from the remainder of the outer surface, and liquid paint of a second color is sprayed thereon. Next, the recessed region of the workpiece is masked off from the non-recess region, and liquid paint of a third color is sprayed onto the recessed region. Clear powder coating material is thereafter applied over the entire outer surface of the workpiece and cured in an oven. The clear coating serves to give the outer surface durability. This is important since liquid paint coatings lack durability and are easily chipped and scratched.
This prior art process has been found to be disadvantageous because it employs liquid paints which include volatile solvents that evaporate into the atmosphere and, thus, risk harm to the environment. The process is furthermore disadvantageous since it requires the additional step of adding a clear coating onto the outer surface of the workpiece, thereby increasing the cost of the process.
Accordingly, there is a need for a method and apparatus for efficiently removing electrostatically bonded powder coating material from a non-recessed region of a surface of a workpiece without also removing powder coating material from a recessed region of the workpiece.